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Old 02-11-2021, 04:57 PM   #1
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Brand: Starcraft
State: Texas
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THOR #22141
Atwood AFMD35121 furnace

Furnace lights, but low heat output and exhaust exhaust soot.
Anyone know how to adjust air mixture?

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Old 02-11-2021, 05:09 PM   #2
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Brand: Thor Motor Coach
Model: FW Hurricane 33T
State: England
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Originally Posted by earlbieler@gmail.com View Post
Furnace lights, but low heat output and exhaust exhaust soot.
Anyone know how to adjust air mixture?
From the Service Manual - SOOT (caused by lazy yellow flame)

LAZY FLAME (yellow)

High gas pressure - Set gas pressure to a minimum of 11Ē W.C. with all appliances running replace regulator, if not obtainable. Also, check main burner orifice, it must comply with furnaceís specifications

Burner out of adjustment Adjust burner according to furnace specification

Combustion wheel installed backwards or loose (warranty covered only when improperly installed at the factory)Reposition wheel and tighten

Air leakage at gaskets Replace gaskets

Low voltage Correct power supply
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Old 02-11-2021, 07:09 PM   #3
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Brand: Thor Motor Coach
State: Missouri
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THOR #6903
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Originally Posted by OldWEB View Post
From the Service Manual - SOOT (caused by lazy yellow flame)

LAZY FLAME (yellow)

High gas pressure - Set gas pressure to a minimum of 11Ē W.C. with all appliances running replace regulator, if not obtainable. Also, check main burner orifice, it must comply with furnaceís specifications

Burner out of adjustment Adjust burner according to furnace specification

Combustion wheel installed backwards or loose (warranty covered only when improperly installed at the factory)Reposition wheel and tighten

Air leakage at gaskets Replace gaskets

Low voltage Correct power supply
Great summary

To the OP, does your cook top appear to have the correct pressure with burners normal on high? If so LP pressure is correct and it is one of the above
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Old 02-11-2021, 07:16 PM   #4
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Brand: Starcraft
State: Texas
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THOR #22141
The stove, water heater and fridge are all operating normally, all original parts in furnace.
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Old 02-11-2021, 07:29 PM   #5
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Air most likely, could have a nest in the mixing tube

Take it apart and check it all out, noting the air mixture setting
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Old 02-11-2021, 10:14 PM   #6
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Originally Posted by lwmcguire View Post
Air most likely, could have a nest in the mixing tube
Take it apart and check it all out, noting the air mixture setting
Hey yeah, that is a good one that should be in the manual.
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